lactose metabolism

乳糖代谢
  • 文章类型: Journal Article
    我们报告了干酪乳杆菌LC130的完整基因组序列,该序列是从健康的人类粪便样品和NORDBIOTIC集合的一部分中分离的。LC130的2.969Mb基因组包括可能参与乳糖代谢和细菌素产生的基因,肽酶,和多胺,提示潜在的健康益处。
    We report the complete genome sequence of Lacticaseibacillus casei LC130, isolated from a healthy human fecal sample and part of the NORDBIOTIC collection. The 2.969 Mb genome of LC130 includes genes potentially involved in lactose metabolism and the production of bacteriocins, peptidases, and polyamines, suggesting potential health benefits.
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  • 文章类型: Journal Article
    识别和克服阻碍化学品高效高产生产的限制仍然是代谢工程中的重要任务。为了重新连接谷氨酸棒杆菌以生产乙醇,在葡萄糖上使用静息细胞时,我们获得了低产量(理论值的63%),生成大量的琥珀酸酯和乙酸酯。为了防止副产物的形成,我们敲除苹果酸脱氢酶,用大肠杆菌取代丙酮酸脱氢酶复合物(PDHc)的天然E3亚基,只有在有氧条件下才有活性。然而,这种篡改导致糖酵解通量降低了10倍,NADH/NAD比率大大提高。当我们用果糖代替葡萄糖时,我们发现糖酵解通量大大增强,这使我们推测还原力的来源是否可能是果糖代谢时绕过的磷酸戊糖途径(PPP)。的确,在通过删除zwf基因关闭PPP之后,编码葡萄糖-6-磷酸脱氢酶,葡萄糖的乙醇产量显著增加,92%的理论。基于此,我们设法将谷氨酸棒杆菌的代谢以高产率重新转化为d-乳酸,98%,这是报告中最高的。它进一步证明,PPP灭活的平台菌株可以提供高产量生产的有价值的化学品,使用包含在乳制品废物作为原料的乳糖,这为可能将乳制品废物转化为有价值的产品铺平了一条有希望的道路。重要性广泛使用的工业主力谷氨酸棒杆菌在非生长条件下具有复杂的无氧代谢,我们在此证明了静息谷氨酸棒杆菌中的PPP是还原力的来源,可以干扰其他氧化还原平衡的代谢途径并降低所需产物的产量。通过利用这种生理洞察力,我们使用PPP灭活的平台菌株生产乙醇,d-乳酸,和丙氨酸使用乳品废物乳清渗透物作为原料。产量高,我们的结果表明,当目的是使用非生长的谷氨酸棒杆菌细胞生产有价值的化合物时,静息细胞中PPP通量的失活是一种有前途的策略。总的来说,我们描述了在非生长的谷氨酸棒杆菌中破坏氧化PPP的好处,并提供了一种可行的废物增值方法。
    Identifying and overcoming the limitations preventing efficient high-yield production of chemicals remain important tasks in metabolic engineering. In an attempt to rewire Corynebacterium glutamicum to produce ethanol, we attained a low yield (63% of the theoretical) when using resting cells on glucose, and large amounts of succinate and acetate were formed. To prevent the by-product formation, we knocked out the malate dehydrogenase and replaced the native E3 subunit of the pyruvate dehydrogenase complex (PDHc) with that from Escherichia coli, which is active only under aerobic conditions. However, this tampering resulted in a 10-times-reduced glycolytic flux as well as a greatly increased NADH/NAD+ ratio. When we replaced glucose with fructose, we found that the glycolytic flux was greatly enhanced, which led us to speculate whether the source of reducing power could be the pentose phosphate pathway (PPP) that is bypassed when fructose is metabolized. Indeed, after shutting down the PPP by deleting the zwf gene, encoding glucose-6-phosphate dehydrogenase, the ethanol yield on glucose increased significantly, to 92% of the theoretical. Based on that, we managed to rechannel the metabolism of C. glutamicum into d-lactate with high yield, 98%, which is the highest that has been reported. It is further demonstrated that the PPP-inactivated platform strain can offer high-yield production of valuable chemicals using lactose contained in dairy waste as feedstock, which paves a promising way for potentially turning dairy waste into a valuable product.IMPORTANCE The widely used industrial workhorse C. glutamicum possesses a complex anaerobic metabolism under nongrowing conditions, and we demonstrate here that the PPP in resting C. glutamicum is a source of reducing power that can interfere with otherwise redox-balanced metabolic pathways and reduce yields of desired products. By harnessing this physiological insight, we employed the PPP-inactivated platform strains to produce ethanol, d-lactate, and alanine using the dairy waste whey permeate as the feedstock. The production yield was high, and our results show that inactivation of the PPP flux in resting cells is a promising strategy when the aim is to use nongrowing C. glutamicum cells for producing valuable compounds. Overall, we describe the benefits of disrupting the oxidative PPP in nongrowing C. glutamicum and provide a feasible approach toward waste valorization.
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  • 文章类型: Journal Article
    When Streptococcus mutans is transferred from a preferred carbohydrate (glucose or fructose) to lactose, initiation of growth can take several hours, and substantial amounts of glucose are released during growth. Here, S. mutans strains UA159 and GS-5 were examined for stochastic behaviors in transcription of the lac operon. Using a gfp reporter fusion, we demonstrated that induction of the lac operon occurs in only a fraction of the population, with prior exposure to carbohydrate source and strain influencing the magniture of the sub-population response. Lower glucokinase activity in GS-5 was associated with release of substantially more glucose than UA159 and significantly lower lac expression. Mutants unable to use lactose grew on lactose as the sole carbohydrate when strains with an intact lac operon were also present in the cultures, indicative of the potential for population cheating. Utilizing a set of engineered obligate cheating and non-cheating strains, we confirmed that cheating can sustain a heterogeneous population. Futher, obligate cheaters of GS-5 competed well with the non-cheaters and showed a high degree of competitive fitness in a human-derived consortium biofilm model. The results show that bet-hedging behaviors in carbohydrate metabolism may substantially influence the composition and pathogenic potential of oral biofilms.
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  • 文章类型: Journal Article
    Revealing the metabolic profiles of carbohydrates with their regulatory genes and metabolites is conducive to understanding their mechanism of utilization in Streptococcus thermophilus MN-ZLW-002 during pH-controlled batch fermentation. Transcriptomics and metabolomics were used to study carbohydrate metabolism. More than 200 unigenes were involved in carbohydrate transport. Of these unigenes, 55 were involved in the phosphotransferase system (PTS), which had higher expression levels than those involved in ABC protein-dependent systems, permeases, and symporters. The expression levels of the genes involved in the carbohydrate transport systems and phosphate transport system were high at the end-lag and end-exponential growth phases, respectively. In addition, 166 differentially expressed genes (DEGs) associated with carbohydrate metabolism were identified. Most genes had their highest expression levels at the end-lag phase. The pfk, ldh, zwf, and E3.2.1.21 genes involved in the glycolytic pathway had higher expression levels at the end-exponential growth phase than the mid-exponential growth phase. The results showed high expression levels of lacZ and galKTM genes and reabsorption of extracellular galactose. S. thermophilus MN-ZLW-002 can metabolize and utilize galactose. Overall, this comprehensive network of carbohydrate metabolism is useful for further studies of the control of glycolytic pathway during the high-density culture of S. thermophilus.
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  • 文章类型: Comparative Study
    Streptococcus infantarius subsp. infantarius (Sii) and Streptococcus gallolyticus subsp. macedonicus are members of the Streptococcus bovis/Streptococcus equinus complex (SBSEC) associated with human infections. SBSEC-related endocarditis was furthermore associated with rural residency in Southern Europe. SBSEC members are increasingly isolated as predominant species from fermented dairy products in Europe, Asia and Africa. African variants of Sii displayed dairy adaptations to lactose metabolism paralleling those of Streptococcus thermophilus including genome decay. In this study, the aim was to assess the prevalence of Sii and possibly other SBSEC members in dairy products of East and West Africa in order to identify their habitat, estimate their importance in dairy fermentation processes and determine geographic areas affected by this potential health risk. Presumptive SBSEC members were isolated on semi-selective M17 and SM agar media. Subsequent genotypic identification of isolates was based on rep-PCR fingerprinting and SBSEC-specific16S rRNA gene PCR assay. Detailed identification was achieved through application of novel primers enhancing the binding stringency in partial groES/groEL gene amplification and subsequent DNA sequencing. The presence of S. thermophilus-like lacS and lacZ genes in the SBSEC isolates was determined to elucidate the prevalence of this dairy adaptation. Isolates (n = 754) were obtained from 72 raw and 95 fermented milk samples from Côte d\'Ivoire and Kenya on semi-selective agar media. Colonies of Sii were not detected from raw milk despite high microbial titers of approximately 10(6)CFU/mL on M17 agar medium. However, after spontaneous milk fermentation Sii was genotypically identified in 94.1% of Kenyan samples and 60.8% of Kenyan isolates. Sii prevalence in Côte d\'Ivoire displayed seasonal variations in samples from 32.3% (June) to 40.0% (Dec/Jan) and isolates from 20.5% (June) to 27.7% (Dec/Jan) present at titers of 10(6)-10(8)CFU/mL. lacS and lacZ genes were detected in all Kenyan and 25.8% (June) to 65.4% (Dec/Jan) of Ivorian Sii isolates. Regional differences in prevalence of Sii and dairy adaptations were observed, but no clear effect of dairy animal, fermentation procedure and climate was revealed. Conclusively, the high prevalence of Sii in Kenya, Côte d\'Ivoire in addition to Somalia, Sudan and Mali strongly indicates a pivotal role of Sii in traditional African dairy fermentations potentially paralleling that of typical western dairy species S. thermophilus. Putative health risks associated with the consumption of high amounts of live Sii and potential different degrees of evolutionary adaptation or ecological colonization require further epidemiologic and genomic investigations, particularly in Africa.
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